The present invention relates to disc drive storage systems and, more particularly, to a disc head slider having rails with trailing edge cuts.
Disc drives of the "Winchester" type are well known in the industry. Such drives use rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers which write information to and read information from the disc surfaces. An actuator mechanism moves the sliders from track to track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a suspension for each head gimbal assembly. The suspension includes a load beam and a gimbal. The load beam provides a preload force which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc. The slider includes an air bearing surface which faces the disc surface.
There are generally two types of sliders, positive pressure air bearing (PPAB) sliders and self-loading or "negative pressure" air bearing (NPAB) sliders. An NPAB slider typically has a pair of rails extending along the sides of the bearing, with a cavity dam extending between the rails near the leading end of the slider. As the disc rotates, the surface of the disc drags air under the cavity dam by viscous friction exerted by the disc surface. As the air passes over the cavity dam, the air expands into a "cavity" between the rails, which forms a partial vacuum in the cavity. The partial vacuum draws the slider closer to the disc surface and counteracts positive pressure developed along the rails. The cavity is open to atmospheric pressure at the trailing end of the slider, and may also include a center rail or an island at the trailing end of the slider to mount a single recording head. NPAB surfaces have many advantages, such as reduced take off and landing velocity during spindle start up and shut down, high bearing stiffness and lower sensitivity of flying height to changes in altitude and velocity, as compared to PPAB sliders having no cavity dam.
However, NPAB sliders are seldom used in ramp "load-unload" drive applications because of their high suction force. In these applications, the slider is unloaded from the disc surface by rotating the actuator mechanism until the suspension engages a ramp which lifts the suspension and thus the slider from the disc surface. The high suction force prevents an NPAB slider from following the suspension as the suspension rides up on the unloading ramp. The slider remains in close proximity to the spinning disc causing the ramp to elastically deform the suspension. The NPAB suction force breaks only when a significant elastic strain has accumulated in the suspension. The release of the suction force releases the elastic strain in the suspension and allows the slider to unload from the disc surface. This cycle of suction force and strain release occurs very rapidly relative to the time in which the suspension is in contact with the unloading ramp. The rapid release of elastic strain energy sets up vibratory oscillations in the slider position coordinate that is normal to the plane of the disc surface. These oscillations may be large enough to cause the slider to "slap" against the disc surface, thereby generating wear debris particles and possibly damaging the recording head.
Another problem observed with NPAB sliders during unloading occurs in the event that the unloading force exerted by the deformed suspension is too small to overcome the suction force. In this event, the suction force is broken when the slider is swung over the disc perimeter, allowing the atmosphere to flow into the cavity between the side rails with very little resistance. As the slider passes over the disc perimeter, pressurization between the side rails becomes unbalanced, causing the slider to roll to one side. As a result, the slider may contact the disc perimeter when unloading. Repetition of such contact causes wear on the slider and generates debris particles.
In contrast, PPAB sliders have a low suction force, making them more applicable for ramp load-unload drive applications than NPAB sliders. Although the side rails in a PPAB slider are not connected by a cavity dam, some air expansion typically occurs as the air is dragged under slider, if the slider has side rails with wide leading ends that transition to a narrow sections near the middle of the slider. The suction force due to these expansions is somewhat smaller than that obtained with the expansion over a cavity dam in an NPAB slider, which allows PPAB sliders to be used more effectively in ramp load-unload applications. In certain PPAB sliders designs, however, the suction drawn at the disc OD may be large enough to result in an undesirably low flying height at the disc OD and adverse effects on unloading performance.
Sliders having "hour glass" shaped rails have been used to counteract the reduction in flying height at the disc OD by reducing the effects of skew. An hour glass shaped rail has wide leading and trailing ends and a narrow waist section. In a typical 3.0 inch disc drive, the skew angle at the disc OD is larger in absolute value than the skew angle at the disc ID. Therefore, hour glass shaped rails tend to increase the flying height at the disc OD relative to the flying heights at the disc ID and the disc MD. However, the flying height at the disc middle diameter (MD) becomes significantly higher than at the disc ID and at the disc OD. This is typically quantified as the "MD hump" which is defined as the MD flying height minus the average of the ID and OD flying heights. A typical MD hump is over 0.3 microinches. An MD hump of this magnitude degrades the recording performance at the disc MD due to fringing field losses in the air gap between the magnetic recording head and the disc surface.